The present invention relates to a machine for forming articles of glass or similar thermoplastic materials. More particularly, it relates to a transport unit which transports along a predetermined path neck molds including neck rings each composed of two neck ring halves, wherein each neck ring half hangs on a holding element and each holding element displaces relative to guiding bars of a transport element by a drive element between closed and open end positions and locks by a locking mechanism in the end positions. Transport units of the abovementioned general type are known, for example, from the German Pat. No. 1,596,472 (FIGS. 7-16) and the German Auslegeschrift No. 1,704,112 (FIGS. 8-10) as well as in the corresponding U.S. Pat. Nos. 3,622,305 and 3,644,111. In this transport unit the holding elements are mounted displaceably directly on the guiding bars. Exchange, repair and maintenance of the holding elements and the neck molds are time consuming and lead to undesirable stopping of the machine.